1. Field of the Invention
The present invention relates to an electromagnetic actuator that uses a coil and permanent magnets.
2. Description of the Related Art
A linear electromagnetic actuator is known, which enables generation of magnetic saturation in a yoke to be suppressed, by forming first and second projections that face toward a guide rail from both sides of a slide table (see, Japanese Laid-Open Patent Publication No. 2006-187192).
Because it is required for the guide rail to have significant hardness, the hardness of the guide rail is preserved to a large degree by the materials used, and by heat treatment. However, when the guide rail is fabricated with large hardness, the coercive force as well as hysteresis in the guide rail also becomes greater. As a result, when the permanent magnets move over the guide rail accompanying movement of the slide table, residual magnetization is generated in the guide rail. From the effect of such residual magnetization, braking forces are generated in a direction opposite to the direction of movement of the permanent magnets. As a result of generation of such braking forces, the thrust force in the movement direction becomes smaller. Further, when positioning of the slide table is controlled, the coercive force causes oscillations, and accuracy in positioning of the slide table is deteriorated.